gstamchybris.c: disabling google software codecs

This is until we have software rendering working in mirsink, otherwise
we have a crash in mirsink when copying buffers around.

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Merge pull request #3 from rsalveti/disable-sw-decoders

gstamchybris.c: disabling google software codecs